Systems and Methods for Coordinating the Coverage and Capacity of a Wireless Base Station

ABSTRACT

A communications base station is installed at a selected new location and the base station, prior to going “online” monitors the wireless traffic from other base stations within interference range of the new base station&#39;s coverage area. The new base station also monitors the wireless traffic between mobile devices within its coverage area and these other base stations. Based upon these monitored conditions, as well as other known conditions, the new base station then determines the transmitting parameter configuration it should imply in order to achieve a desired optimization between capacity and coverage area. After the new base station is online, a central control can monitor the entire network to determine if any additional changes are necessary and if so the new transceiver, or any other transceiver, can be instructed to monitor itself with respect to interference and to take corrective action to improve overall network coverage and capacity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a continuation of U.S. patent application Ser. No.12/651,820, filed Jan. 4, 2010 and entitled “SYSTEMS AND METHODS FORCOORDINATING THE COVERAGE AND CAPACITY OF A WIRELESS BASE STATION,”which is a division of U.S. patent application Ser. No. 11/097,095,filed Apr. 1, 2005 and entitled “SYSTEMS AND METHODS FOR COORDINATINGTHE COVERAGE AND CAPACITY OF A WIRELESS BASE STATION,” which issued Feb.23, 2010 as U.S. Pat. No. 7,668,530, the disclosures of which areincorporated herein by reference.

TECHNICAL FIELD

This invention relates to wireless communication and more particularlyto systems and methods for increasing base station coverage and capacityin a wireless network, and even more particularly to such methods andsystems for placement of wireless transceivers within a communicationnetwork.

BACKGROUND OF THE INVENTION

One problem experienced in wireless communication systems is locatingbase stations. Once a base station (transmitter/receiver) is positionedin a coverage area it is important to be able to set its respectiveparameters in order to provided the desired coverage or capacity.

In this context, coverage is the geographical area covered by thesignals to or from the base station while capacity relates to the amountof data that can pass through the base station to or from mobiledevices. Base stations can be optimized for either coverage area orcapacity (throughput). Typically, such optimization has beenaccomplished by using a sophisticated set of tools that are available tothe wireless network designer. These tools would provide signalpropagation models to the designer for use in calculating coverage areasfor a particular base station. The designer would also estimate theinterference that could result with respect to mobile devicescommunicating with a different base station some distance away, so thesemay or may not be on the same channel.

In some wireless networks the various base stations would use differentchannels or frequencies to avoid interference issues. Wireless networkfrequency planning is used to avoid, or minimize, such interferenceproblems between adjacent and nearby base stations.

In newer wireless systems, such as, for example, orthogonalfrequency-division multiplexing (OFDM) and orthogonal frequency-divisionmultiple access (OFDMA), the tendency is to overlap frequencies andchannels across base stations and to eliminate interference by assigningdifferent combinations of sub-channels (sub-carriers) to differentmobile devices communicating at the same time. These modulation schemesallow variable data rates and variable amounts of robustness in terms ofbeing able to tolerate the interference. The ideal system is one inwhich a base station can serve a high number of mobile devices with nointerference between devices. In order to achieve such an ideal systemit is important that each communicating mobile device has a strongsignal. If, on the other hand, there are two mobile devices each on theedge of coverage with two base stations and if propagation were uniform,those mobile devices would most likely experience interference. Thisinterference would reduce the data rate for those devices in order toprotect the integrity of the data.

Turning to the problem of location of a new transmitter/receiver (hereincalled a transceiver) the network designer, as discussed above, decideson a location, has the transceiver erected and installed and then tunesit up by adjusting the power level, the elevation angle of the antenna,etc. in accordance with the precalculated plan for this transceiver.Once these adjustments are made, the transceiver is turned on and “seeswhat actually happens.” The technician can then readjust the powerlevels, adjust the down tilt of the antenna, and possibly swap out theantenna with an antenna having a different azimuth angle. If thetransceiver continues to cause interference, or not properly cover thedesignated area network, adjustments might have to be made, or the powerlevel reduced further. In some instances the adjacent base stations alsoneed to be read.

BRIEF SUMMARY OF THE INVENTION

A communications base station is installed at a selected new locationand the base station, prior to going “online” monitors the wirelesstraffic from other base stations within interference range of the newbase station's coverage area. The new base station also monitors thewireless traffic between mobile devices within its coverage area andthese other base stations. Based upon these monitored conditions, aswell as other known conditions, the new base station then determines thetransmitting parameter configuration it should apply in order to achievea desired optimization between capacity and coverage area.

After the new base station is online, a central control can monitor theentire network to determine if any additional changes are necessary andif so the new transceiver, or any other transceiver, can be instructedto monitor itself with respect to interference and to take correctiveaction to improve overall network coverage and capacity.

In one embodiment, operating power levels are gradually raised as thenew base station comes online so as to minimize interference. Inaddition, if desired, the new base station can automatically adjust itsantenna beams in elevation, pointing angle and beam width.

In one embodiment, the new base station would determine the most optimumoperating parameters for its use, and if those parameters causeinterference in the network then a central control will assist in theadjustment of the network to achieve the optimization of the entirenetwork.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims. The novel features which are believed to be characteristic ofthe invention, both as to its organization and method of operation,together with further objects and advantages will be better understoodfrom the following description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying drawings, in which:

FIG. 1A shows one embodiment of a wireless network where a base stationis being added;

FIG. 1B is a chart illustration of the before and after characteristicsat certain locations within the coverage area of the wireless network;

FIG. 2 is a flow chart illustrating one embodiment of the invention; and

FIG. 3 is an illustration of one embodiment of the inventiondemonstrating coverage areas.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A shows wireless network 10 initially having one base station 11with coverage area defined by dotted line 12. Transmission and othercontrol to/from base station 11 is controlled by base station controller121 in conjunction with central control (NOC) 120 which could beco-located with a base station, if desired. Contained within basestation controller 121 is a database and at least one software programwhich controls transmission to/from the base station as is now wellknown. As will be seen, while transmission from base station 11 can, intheory, reach out to point 104, transmissions to and from that locationwould most probably be unsatisfactory because of low energy. Sincemobile devices, such as cell phones, personal digital assistants (PDAs),computers, two-way pagers and the like, do not transmit with as muchenergy as does a base station, most wireless devices would not be ableto transmit as far as does the base station and thus the actual coveragearea would be even less than shown by dotted line 12.

In FIG. 1A, there are three points of interest, 101, 102, and 103, thatwill be examined. However, the concepts that we will be discussing areapplicable over the entire coverage area, varying only in degree. Alsonote that while certain network types, such as OFDM and OFDMA networks,will be discussed, the concepts discussed herein can be applied to manynetwork types.

An OFDM network contains many (256-1024 being typical) orthogonalcarriers. In such a system, subcarrier aggregations are formed(typically in the order of 16 to 32) for each communication connectionin order to decrease interference and thus increase capacity(throughput). In order to support many more active users, thesubcarriers may be time-shared and reassigned to different mobilestations on a frame by frame basis with a typical frame being 5 ms. Insuch systems, it is possible for several mobile devices to share some(but not all) of the carriers used by the other devices. If thesubcarriers that make up a particular connection are properly selected,interference between the mobile devices is reduced to a minimum. A morecomplete description of an OFDM system is contained in “OFDM forWireless Multimedia Communications” by Richard D. J. Van Nee and RamjeePrasad (ISBN 0890065306) which is hereby incorporated by referenceherein. In addition, the following references, which are herebyincorporated by reference herein, are useful for calculating propagationloss: “Field Strength and Its Variability in VHF and UHF Land-MobileRadio Service,” by Yoshihisa Okumura, et al., Review of the ElectricalCommunications Laboratory, Vol. 16, No. 9-10, September-October 1968 andHata “Empirical formula for propagation loss in Land Mobile radioservices,” IEEE Transactions on Vehicular Technology, Vol. 29, No. 3,Aug. 1980.

When a need arises for a new base station, either by an increase inwireless usage in an area or by the construction of a structure blockingexisting transmissions, engineering calculations are made to determinethe most effective possible sites. These calculations take into accounta myriad of factors, including the amount of added capacity and amountof added coverage area desired. However, while the engineering factorsare important, other factors, such as availability of land and theability to obtain governmental and regulatory approvals must also beconsidered. Once the new location, for example location 110, FIG. 1, isdecided upon for a base station (transceiver), the base station isconstructed at that site.

The procedure that has been followed in the past when a base station isready to go online is that the antennas are set to achieve thecalculated distances and radiation pattern and the transceiver “lightsup” (goes online) and begins to transmit. Calculations are then made asto interference and other factors. Adjustments are then made to thepower levels, frequencies are changed, antenna tilt (either physicallyor electronically) as well as other factors are adjusted to make surethe new base station does not interfere with, for example, transmissionto/from base station 11. Often the results are confirmed by extensiveand tedious drive testing.

Based upon the concepts discussed herein, new base station 13 isconstructed at location 110, but prior to coming online, new basestation (NBS) 13 performs at least two functions. The first function isthat it monitors the wireless traffic from other base stations withininterference range of the coverage area of the transceiver. The secondfunction performed is to monitor wireless traffic between the mobiledevices within its coverage area of its base station and other basestations to determine what level of coverage is available.

For example, as shown in FIG. 1B, base station 13 would monitor trafficin the region of 101 and find that there is good coverage from existingbase station 11 and into area 101 there would possibly be interferencebetween the two base stations.

Base station 13 would monitor region 102 and determine that there ismarginal coverage from transceiver 11 that with the conclusion area 102is an area that base station 13 should cover. Base station 13 also looksat region 103 and determines that wireless devices in that area are notbeing properly served with the conclusion that area 103 would be a goodcoverage area for transceiver 13.

This procedure is followed for a period of time until new base station13 understands the coverage areas and the transmissions from differentcommunication devices within its area. At that point, base station 13“lights up” and goes online. Once online, base station 13 can monitorthe traffic to see if, in fact, there is an unanticipated interference.In some situations central control 120, which can be part of any basestation or could be a separate stand alone control center, can receivesignals and measurements from a plurality of base stations and canoperate to send adjustment commands to one or more of the base stationsasking the base stations to change their coverage area power level,frequency, or even their mode of operation. Note that because trafficpatterns change by time of day and between weekday and weekend, basestation 13 could be setup as an average “best effort” configuration.Also note that base station 13 (or any base station using the conceptsdiscussed herein) can maintain in memory sets of parameters suitable forsuch different times (busy hours, day/night, weekday, weekend,emergency, etc.) and can then adjust the parameter of the NBS to bestsuit those times.

After new base station 13 has come online other base stations could, ifdesired, perform the same monitoring functions and adjust themselves soas to optimize the network. This optimization can be on a periodic basisor under certain triggers such as when a certain number of calls aredropped or when a certain number of mobile stations report highinterference levels. Control would be required between base stations sothat the base stations do not interact with each other to cause adestabilization of the network.

FIG. 2 shows one embodiment 20 of a flow chart illustrating the “plugand play” nature of the addition of a new base station and illustratesone example of bringing a new base station online. Process 201 controlsthe New Base Station (NBS) so that it tunes to all the base stationemissions within the coverage area. The NBS tunes to the other basestation frequencies and/or timeslots. This is done to begin the mappingprocess with respect to signals and interference in and around the NBS.The NBS measures received power from all base stations where the poweris above the noise threshold or other set thresholds. This is necessaryso that the NBS knows what devices are in its coverage area and whatfrequencies are involved. Some of the information obtained by the NBScomes from central control (NOC) 120 and is used to calculate:

a. a path loss to the NBS from each base station (BS);

b. a predicted path loss of a mobile station (MS) within the NBS rangeto each BS (formula); and

c. a path loss (PL) vs distance function (this may be angle dependant)for an assumed MS in communication with the NBS (formula, model).

Process 202 measures the signal levels of each channel at each basestation. A log is made of the frequencies and power levels that arereceived at the NBS from the nearby BSs.

Process 203 rank orders the signal levels by power or by any otherparameter desired. For example, a power rank order list is compiledwhich provides a first indication of what channels the BS may select,the weakest signals being the most likely selections.

Process 204 tunes and monitors transmission mobile station transmissionsfor X hours and associates each mobile station with a particular basestation. A data set is collected by monitoring and aggregating thereceived powers from a host of MS. The NBS knows from the NOC thechannels and their associated BS locations. This monitoring is so thatthe new base station gets a picture of the transmissions to and frommobile stations and who they are in communication with and can take froma few hours to several days to obtain a fair picture of wirelesstraffic. The actual time depends on the accuracy required.

Process 205 computes the mobile station receive signal leveldistribution for each base station by calculating the power received ata MS and from a MS and BS at any given distance from the NBS. The MSassociated with each BS is knowable because of unique frequencies,timeslots and other pilot addressing schemes as provided by a standard(e.g., IEEE 802.16a). For each BS there will be a distribution of MSsignal levels due to their various locations. The NBS calculates theexpected maximum distance that a MS can be from the NBS based on the NBSpotential available power antenna gain, height, terrain parameters, etc.The NBS also calculates the expected distance of a MS from the NBS wherethe Signal to Interference Ratio (SIR)=1. That is a MS receives equalpower from the NBS and the strongest existing BS on the same channel.

This is shown by illustration 30, FIG. 3. The strongest BS is BS (1) andrange A′-B′ is the useable range where SIR=1 (i.e. the signal andinterference are equal). Range C would be the range of the NBS ifinterference were not a factor. Note that range C will vary based on thetransmitting parameters, (power, frequency, tilt, pattern, polarization,etc.) of the NBS, as well as terrain, foliage, buildings, etc.

In process 206 the operator has previously input a set of goals (e.g.,increase capacity in a certain area). This calculates into idealsettings for constant W, Y and Z to be used in the signal flow below.Process 206 adjusts the NBS in accordance with these system goals orrequirements. This step requires a service provider assisted goal, forexample. A goal could be to: Expand the range until SIR at mobile equalsX dB (0, +3, +6, negative is generally not useful as the other BS shouldhandle the MS unless that BS is full). An alternative goal could be to:Expand the range until a predetermined amount of traffic is acquiredwithin a given range. Further optimization can be achieved by adjustingsector pattern and downtilt. For example, the NBS can expand inbeamwidth to increase traffic or it can increase downtilt to reduceinterference inside the coverage area.

Process 207 determines if there is a channel where mobile station andsignals are below a certain dB level Y. The parameter Y may be set verylow so that the most ideal channel is found. If the answer is yes, thenat least temporarily base station 13 assigns itself that channel viaprocess 208 and could at this point come online process 404, at leastwith respect to that channel. In this context, it could be a channel ora set of sub-channels or any combination thereof.

If the criteria of process 207 cannot be met, a reduced requirement istested. In process 210 if certain percentage W of the MS meet thecriteria, that channel is assigned (process 211) and the BS broughtonline at process 209.

If the answer is no in process 210 (i.e., even the reduced criteria arenot met) then process 212 determines if there is a subset of channelsavailable. If the answer at process 210 is yes, the base station willassign itself those subsets via process 213, and a reduced capacity HBSis brought online (process 209). If the answer is no, at process 212then a new set of requirements are rendered (new Y, Z and W in ourexample) via process 214 and processes 406-414 are repeated until theNBS is operational.

The new requirement could, for example, be a change of transmissionparameters from other BSs under control of NOC 120 by adjusting BS powerand antenna parameters to reduce interference or increase systemcapacity. Also, the NBS can refine its estimate of pathloss based onranging information from MS after it “lights up.” This is based on thefact that a MS will choose a BS based on the strongest pilot signal theMS receives, the NBS can determine from time of arrival data(distributions) the range of actual MS. Accordingly, the NBS can adjustpower and/or antenna parameters to more closely match the desiredcoverage.

The logic flow may readily be extended (line 220) after the NBS isturned on to monitor, for example, the increased traffic versus thetransceiver signal power or versus antenna downtilt.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods and steps described in the specification. Asone of ordinary skill in the art will readily appreciate from thedisclosure of the present invention, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present invention.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

1. A method for optimizing service in a wireless network, said methodcomprising: calculating, at a first base station, a set of transmissionparameters for a second base station, said transmission parameterscalculated to achieve service criteria; receiving, at said first basestation, signals from said second base station corresponding tomeasurements made by said second base station, said measurements basedon wireless communication between said second base station and a mobilestation; and transmitting, from said first base station, a command tosaid second base station, said command comprising an adjustment to bemade by said second base station to achieve said criteria.
 2. The methodof claim 1 wherein said command comprises an adjustment of coverage areapower level, frequency, or mode of operation.
 3. The method of claim 2wherein said command is dependent upon time of day or day of week.